In recent years, a computer to plate system (CTP), in which an image data can be directly recorded in a printing plate material, has been widely used accompanied with the digitization of printing data. As a printing plate material usable for CTP, there are a printing plate material comprising an aluminum support such as a conventional PS plate, and a flexible printing plate material comprising a flexible resin film sheet and provided thereon, various functional layers.
Recently, in commercial printing industries, there is a tendency that many kinds of prints are printed in a small amount, and a printing plate material with high quality, which is inexpensive, has been required in the market. As a conventional flexible printing plate material, there are a silver salt diffusion transfer type printing plate material as disclosed in Japanese Patent O.P.I. Publication No. 5-66564, in which a silver salt diffusion transfer type light sensitive layer is provided on a flexible sheet, an ablation type printing plate material as disclosed in Japanese Patent O.P.I. Publication Nos. 8-507727, 6-186750, 6-199064, 7-314934, 10-58636 and 10-244773 in which a hydrophilic layer and a lipophilic layer, one of which is an outermost layer, are provided on a flexible sheet where the outermost layer is ablated by laser exposure to prepare a printing plate, and a heat melt type printing plate material as disclosed in Japanese Patent O.P.I. Publication No. 2001-96710 in which a hydrophilic layer and a heat melt image formation layer are provided on a flexible sheet where a hydrophilic layer or a heat melt image formation layer is imagewise heated by laser exposure to heat fix the image formation layer onto the hydrophilic layer.
The silver salt diffusion transfer type printing plate material requires a wet development step and a drying step after exposure, which does not give sufficient dimensional accuracy during the image formation step. The ablation type printing plate material does not require a wet development step, but image formation due to ablation is likely to fluctuate in dot shape. Further, there is problem in which the interior of the exposing apparatus or the printing plate surface is contaminated by scattered matters caused by ablation of the layer. The heat melt type printing plate material in which the heat melt image formation layer is fixed onto the hydrophilic layer, after image formation, is mounted on an off-set press. When on printing, a dampening water is supplied to the printing plate material, only the image formation layer at non-image portions is swollen or dissolved by the dampening water, and transferred to a printing paper (paper waste) to remove. Accordingly, a special development step is not required, and image formation due to heat melt provides a sharp dot shape, and prints with high image quality.
When laser exposure is carried out, a flexible printing plate material is generally fixed on a specific position of a flat or curved fixing member of an exposure device, and exposed. As methods of fixing a printing plate material on a fixing member, there are a vacuum fixing method in which a printing plate material is fixed on a fixing member with suction holes under atmospheric pressure, by evacuating air between the plate and the fixing member through the suction holes, a magnetically fixing method in which a printing plate material is fixed on a fixing member with a ferromagnetic surface by magnetic force, and a clamping method in which a printing plate material fixed on a fixing member by mechanically clamping the both edges thereof by clamps.
A printing plate material and a printing plate prepared therefrom according to a silver salt diffusion transfer method are well known, the printing plate material comprising a hydrophilic layer, a silver halide emulsion layer, a physical developing nucleus-containing layer, and a backing layer.
Recently, as color printing spreads, a printing plate material suitable for color printing has been required. Since plural printing plates are employed in the color printing, a printing plate with so-called high register accuracy has been required which does not cause “out of color registration” during printing.
As supports of the planographic printing plate material above for CTP, various ones are known. A printing plate material employing as the support a plastic sheet has been developed in that it is easy to handle and carry (see for example, Japanese Patent O.P.I. Publication Nos. 4-261539 and 5-257287).
However, a silver halide diffusion transfer planographic printing plate material employing as a support a plastic sheet has problems in that printing durability after long term storage and initial ink receptivity are poor, and “out of color registration” during printing, so called “out of register”, is likely to be caused. A planographic printing plate material solving these problems has been eagerly desired.